Aircraft are generically divided into two major classes, fixed wing and rotating airfoil. The former are typically thought of as "airplanes", and derive their lift from the forward motion of the machine, which causes air to pass over an airfoil. Rotary winged aircraft, commonly called "helicopters", have a prime mover attached to an airfoil, which rotates. The primary drawback to conventional aircraft is that they must have rather a large area to take off and land. The principle drawback to the helicopter is that it is extremely expensive to manufacture, has little inherent control stability, and is capable of very low forward speeds, compared to an aircraft having a prime mover of the same power. The most successful short take-off and landing aircraft is the helicopter, whose rotary system produces the necessary lift. To reduce high speed vibration and drag on the rotor, stub wings are sometimes added to produce lift at forward speeds, thereby reducing load on the rotor. The results, in various configurations, are called the convertaplane. In hovering, however, the down wash of the rotor produces large loads on the wings, which compromise hovering performance.
To avoid these difficulties, several alternatives have been tried. These range from tilting the entire aircraft 90.degree. after vertical take-off, as was done with the "Bell Pogo" aircraft, which used counter-rotating propellers on the nose of the aircraft, to tilting the power plant or wings, in combination. The same effect can be obtained by running jet engines in a horizontal position and deflecting the jet blast downward, to effect vertical thrust for take-off. When sufficient altitude has been gained, the deflection vanes are retracted and the aircraft moves in level flight. The most spectacular example of this class is the British Harrier military aircraft, which can rise vertically from area little greater than its own overall dimensions, then achieve supersonic speed in level flight. The process can be reversed for vertical landing.
All direct-lift machines known to the prior art have certain problems in common. The first is the detrimental effect of the high energy slip stream or jet striking the ground. Loose material thrown about constitutes a hazard, both to the machine and to personnel in the vicinity. Also, while the entire lifting force depends upon the engines, power failure can prove catastrophic. The greatest possible reliability in adequate emergency back-up systems is an absolute requirement in order to assure the safety of the machine and its occupants.
Because there is little or no flow over the aerodynamic control surfaces during hovering flight, entirely different types of thrust vector controls have been utilized by V/STOL's during hovering or slow forward flight. As of the early 1980's, none of these systems are entirely satisfactory.
Various V/STOL aircraft have been disclosed in the prior art. U.S. Pat. No. 3,083,935, issued to Piasecki, on Apr. 2, 1963, discloses a convertible aircraft having slidable wing members that move from one position to another position. In one position, the vertical take-off rotors are exposed to the open air. In the other position, the wing provides for aerodynamic forward flight.
U.S. Pat. No. 4,030,688, issued to Pellarini, on June 21, 1977, describes an aircraft structure having a narrow delta planform fuselage with two small-span shoulder type wings in tandem and cascade. The shape of the fuselage and its relationships with the wing provides for the vertical take-off and the forward propulsion capabilities.
U.S. Pat. No. 4,125,232, issued to MacLean et al, on Nov. 14, 1978, discloses a VTOL aircraft with fixed horizontal variable-pitched rotors. The horizontal rotor blades are arranged so as to provide vertical lift for the aircraft. A conventional jet engine is included within this aircraft to provide for horizontal flight.
U.S. Pat. No. 3,335,976 shows an aircraft, like the Ryan XV-5A, incorporating lift fans in the large relatively thick main lift wings and using clamshell shutters to close off the lift wing during forward flight. This design requires thick main wings, which create unacceptable drag during forward flight.
U.S. Pat. No. 4,194,708 teaches the use of a deflectable canard/elevator placed close to the nose tip of the aircraft, with wings mounted low and well aft on the fuselage. U.S. Pat. No. 3,618,875 teaches a V/STOL aircraft having tandem wings containing lift fans, wherein the wings provide only drag during forward flight.
The prior art teaches that, in order to maintain sufficient vertical thrust to operate a VTOL, in-the-wing fans have always necessitated the use of aircraft wings of relatively large area. This has led to the development of many designs such as that shown in U.S. Pat. No. 3,388,878, wherein fuselage mounted lift fans and gas generators lead to very complex retractable lift fan installations. It has been the object of much of the prior art of wing-mounted lift fans to minimize wing area, wing weight and general complexity, because the wings containing the lift fan were not used to provide aerodynamic lift during forward flight. For these reasons, full potential of the lift fan concept has not bee fully realized in V/STOL aircraft designs proposed to date.
U.S. Pat. No. 3,614,030 teaches a disk-like aircraft body forming an access of revolution, wherein individually controlled rotary members movable about the airflow axis control the direction of discharge of air from the ducts. U.S. Pat. No. 3,614,030, however, does not teach an aircraft using conventional aerodynamic lift, but, rather, a ground effect machine.
The present invention relates most closely and is based upon U.S. Pat. 4,469,294, issued on Sept. 4, 1984 to one of the co-inventors of the present invention. This patented device incorporates many of the features of the present invention, but it failed to achieve a truly effective configuration of the inlet and outlet vents relative to the wing fans.
Generally speaking, these, and other prior art proposals, have sought to produce V/STOL aircraft capable of obtaining the vertical flight characteristics of helicopters and the forward flight characteristics of fixed wing aircraft. Such a hybrid provides a potential solution to the air traffic problems of congestion, both in conventional airports and in land transportation to and from conventional airports. The much lower approach speeds of V/STOL aircraft can permit many more aircraft to safely occupy the airspace for multiple take-offs and landings.
It is an object of the present invention to provide a V/STOL aircraft that is relatively inexpensive to manufacture.
It is another object of the present invention to provide a V/STOL aircraft that provides reliable and stable flight.
It is another object of the present invention to provide a V/STOL aircraft that provides for optimal airflow into the lift fan system.
It is still a further object of the present invention to provide a V/STOL aircraft that provides improved fan performance and improved aerodynamic lift.
These and other objects and advantages of the present invention will become apparent from a reading of the attached specification and appended claims.